A one-time friend of Tommy Sheridan has told a perjury trial the former MSP visited a swingers club because he had a "weakness of the flesh".
Dr Nicholas McKerrell also told the High Court in Glasgow he thought Mr Sheridan was "reckless" taking legal action against the News of the World.
Mr Sheridan and his wife Gail, both 46, are accused of perjury.
They deny lying during his successful defamation case against the paper in 2006.
The former leader of the Scottish Socialist Party (SSP) won £200,000 in damages after the newspaper printed allegations about his private life, claiming he was an adulterer who had visited a swingers' club.
Following a police investigation, Mr Sheridan and his wife were charged with perjury.
Glasgow Caledonian University lecturer, Dr McKerrell, said he had known Mr Sheridan since the age of 16, and had joined the SSP in 1998, when it was founded.
The 40-year-old said Mr Sheridan had discussed allegations printed in the News of the World with him before a hustings meeting at the university.
He told advocate depute Alex Prentice QC: "He was quite evasive, he wasn't looking me in the eye, he was looking into his cappuccino.
"He said, 'I think you know a bit about this - that I attended clubs in Manchester twice in 1996 and 2002.'
"Then, he said, 'you know what it's like - weakness of the flesh'."
Dr McKerrell said that the former MSP then mentioned News of the World journalist Anvar Khan, who is alleged to have visited Cupid's swingers club in Manchester with Mr Sheridan.
He said: "He mentioned Anvar Khan. He said Anvar Khan would never testify. He outlined his situation - that he was preparing legal action.
"I thought it was very strange. Tommy was embarking on a reckless course of action that was going to destroy all the work that had been done in the preceding seven years."
Dr McKerrell called suggestions by Mr Sheridan that he was lying a "professional slur".
He said he would be unable to look his students in the eye if he had done that.
He said: "As a law lecturer, I train the future solicitors and advocates of this country.
"How can I look them in the eye if I was guilty of such deceit?"
The trial also heard from Pamela Tucker, who became the fifth person to say they had seen Mr Sheridan at Cupid's.
Ms Tucker said she recognised the former politician because "of what he did with the poll tax".
The 36-year-old said she met Mr Sheridan as she went into the club and later invited him and a group of his friends for a cup of tea before they went home.
She told the court he had to go back "because he had a wife".
She said Mr Sheridan was with another man and two women, one of whom was called Anvar.
Earlier, the trial heard claims the former MSP had accompanied Ms Tucker to buy pizzas after he met her at the swingers club.
She told advocate depute, Alex Prentice QC, her meeting with Mr Sheridan happened in "the cold weather - later September to November".
It is alleged that Mr Sheridan made false statements as a witness in his defamation action against the News of the World on 21 July 2006.
He also denies another charge of attempting to persuade a witness to commit perjury shortly before the 23-day legal action got under way.
Mrs Sheridan denies making false statements on 31 July 2006, after being sworn in as a witness in the civil jury trial at the Court of Session in Edinburgh.
The trial, before Lord Bracadale, continues.